This application is based on Japanese Patent Application No. 11-249317, filed Sep. 2, 1999, the entire contents of which is hereby expressly incorporated by reference.
1. Field of the Invention
The present invention generally relates to valve driving arrangements for outboard motors. More specifically, the present invention relates to an improved compact arrangement of valve driving components.
2. Related Art
Outboard motors are used to power watercraft to the water. The outboard motors are mounted to the transom or rear portion of the watercraft and provide a forward or reverse thrust. Because the outboard motor extends upward above a portion of the watercraft, the outboard is exposed to passing air streams caused by the movement through the water. Accordingly, the outboard motor can be a source of wind resistance or drag during movement through the water. This wind resistance results in decreased watercraft speeds or increased loading on the outboard motor.
Accordingly, it is desired to decrease the size of the exposed portion of the outboard motor. In some configurations, the outboard motors is decreased in a lateral direction while in other arrangements the engine is decreased in a vertical direction. By designing a more compact engine, the overall dimensions of the outer cowling, which surrounds the engine, can be decreased.
With reference now to FIG. 1, a typical outboard motor 10 is illustrated therein. In an effort to decrease the lateral dimension of the outboard motor 10, a pair of cylinder banks 11 have been designed with cylinders 12 that are offset from one cylinder bank to the other. In particular, the engine generally comprises a V-type configuration having a first bank of cylinders 12 and a second bank of cylinders 12. The first bank of cylinders comprises a plurality of cylinders 12 having a corresponding plurality of central axes A that extend through the cylinder bores while the second bank of cylinders is similarly comprised. As will be appreciated, one bank of cylinders is offset by approximately half of the diameter of cylinder bores in the other bank. Such a configuration allows the cylinder and the lateral dimension of the cylinder block to be decreased. This configuration, however, has ordinarily resulted in an increased height to the outboard motor due to an increased vertical dimension required to accommodate a cam shaft drive arrangement 14.
The cam shaft drive arrangement 14 typically uses rotational motion from the crankshaft to drive the intake cam shaft 15 and the exhaust cam shaft 16. The intake cam shaft 15 powers the intake valves while the exhaust cam shaft 16 powers the exhaust valves. Generally, as shown in FIG. 1, power is taken from the crankshaft into one of the intake cam shafts 15 or one of the exhaust cam shafts 16. The power taken from the crankshaft into one of the cam shafts 15, 16 is then transferred to the other of the paired cam shafts 15, 16. For instance, in the illustrated arrangement, power is taken from the crankshaft and transferred to the intake cam shaft 15 of the left cylinder bank and the exhaust cam shaft 16 of the right cylinder bank. The rotational motion then is transferred from the exhaust cam shaft 16 of the right cylinder bank to the intake cam shaft 15 of the right cylinder bank through a drive pulley 17 and a driven pulley 18 that are connected with a flexible transmitter 19, such as a belt. Similarly, power is transferred from the exhaust cam shaft 16 of the left cylinder bank to the intake cam shaft 15 of the left cylinder bank through a drive pulley 17 and a driven pulley 18 that are connected with a flexible transmitter 19.
This arrangement, however, results in the undesirable increase in the vertical dimension of the engine. As illustrated in FIG. 1, the length of the cam shafts 15, 16 in the left cylinder bank must be increased to place the input pulley 13 at an appropriate location relative to the input pulley 13 of the cam shafts 15, 16 of the right cylinder bank. Elongating the cam shafts results in the undesirable increase in the vertical dimension of the outboard motor. In addition, increasing the length of the cam shafts 15, 16 increases the weight of the engine due to the excess material of the cam shaft extension. Furthermore, the strength of the elongated cam shafts must be increased to withstand the loading on the increased length of the cam shaft.
Accordingly, a more compact cam shaft drive arrangement is desired. Such an arrangement desirably should decrease the overall length of at least one set of cam shafts. The cam shaft drive arrangement preferably takes advantage of an offset cylinder configuration.
One aspect of the present invention involves an engine for use in an outboard motor. The engine comprises a pair of cylinder banks. A first set of cylinder bores is disposed in a first cylinder bank of the pair of cylinder banks. A second set of cylinder bores is disposed in a second cylinder bank of the pair of cylinder banks. A first plane is defined through central axes of the first set of cylinder bores and a second plane is defined through central axes of the second set of cylinder bores. The first plane and the second plane intersect at an angle. The engine has a first end surface. A crankshaft has a power take off end that extends through the first end surface. The first set of cylinder bores has a first end cylinder bore and the second set of cylinder bores has a second end cylinder bore. The first end cylinder bore is positioned closer to the first end surface than the second end cylinder bore. A first intake cam shaft and a first exhaust cam shaft are associated with the first cylinder bank and a second intake cam shaft and a second exhaust cam shaft are associated with the second cylinder bank. Power from the crankshaft drives the first intake cam shaft, the first exhaust cam shaft, the second intake cam shaft and the second exhaust cam shaft. The first intake cam shaft and the first exhaust cam shaft are joined by a first drive connection and the second intake cam shaft and the second exhaust cam shaft are joined by a second drive connection. The second drive connection is positioned at an end of the second intake cam shaft and the second exhaust cam shaft that is closest to the first end surface and the first drive connection is positioned at an end of the first intake cam shaft and the first exhaust cam shaft that is farthest from the first end surface.
Another aspect of the present invention involves an engine comprising a crankshaft and a cylinder block that comprises a first cylinder bank and a second cylinder bank. The cylinder block has a first end and an opposing second end. The crankshaft has a power take off end that extends through the first end of the cylinder block. The engine comprises a first set of cam shafts that are associated with the first cylinder bank and a second set of cam shafts that are associated with the second cylinder bank. The first set of cam shafts are coupled for rotation proximate the first end of the cylinder block and the second set of cam shafts are coupled for rotation proximate the second end of the cylinder block.